The Image Processing Toolbox has terminology conventions for four different image types:
- Binary images
- Gray-scale images
- Indexed images
- Truecolor images
You'll also frequently see the term RGB image, which is shorthand for a truecolor image using an RGB color space. (See the User Guide section on image types.)
Over the last few years I've become increasingly dissatisfied with the term truecolor.
Wikipedia has a brief article on truecolor. The article says the term describes a "method of representing and storing graphical image information." It goes on to say that a truecolor representation is one that either:
(a) can represent a large number of colors, typically at least 2^24.
(b) does not use a color look-up table ("colormap" in MATLAB terminology)
Curiously, the article refers to (a) and (b) as "equivalent" statements.
Defining an image representation method in terms of whether it represents a lot of colors is too vague to be very useful in my view. Defining a representation in terms of a characteristic it does not possess (that is, a truecolor representation does not use a color look-up table) is similarly vague.
Also, as I learn more about color science I've grown uncomfortable with the idea that any computer or mathematical representation of color can really be called "true color."
Here's the definition I really want to see:
[blank] is a method of representing image information in which each image pixel is stored as a vector of color-space component values.
But what's a good term to go along with this definition? Help me fill in the blank by commenting with your thoughts.
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